The present invention relates to a screw driving and turning machine by which a screw is driven and then turned to.
In general, the screw driving and turning machine is a type of nailing machine, which includes a driving mechanism to drive a screw and a turning mechanism to turn the screw after driving. Concerning the screw turning mechanism, a conventional mechanism is well known in which a screw, which has been driven by a driver, is turned by the driver being driven by an air motor.
As shown in FIG. 19 in which a conventional structure is illustrated, as a guide means for guiding the screw 30 to be driven, there is provided a guide chuck 231 to guide an end portion of the screw 230 to be driven. In this arrangement, reference numeral 232 is a contact arm.
As shown in FIG. 24(a), the driver 330 is screwed and fixed to the driving piston 331. Alternatively, as shown in FIG. 24(b), the driver 330 is attached into a central hole of the driving piston 331 via the bearing 332.
However, according to the above system in which the time to turn off an air motor switch is determined by an operator who uses his head, the depth of screw engagement is unstably varied. Not only that, the above construction wastes the compressed air.
Furthermore, the following problems may be encountered in the conventional guide mechanism. Since the conventional guide chuck 231 is attached to an end of the nose portion 233, the guide chuck 231 is simultaneously raised when the body is raised by a reaction force in the process of driving. Therefore, an end portion of the bit 234 tends to shift from a groove of the head of the screw 230. As a result, the end portion of the bit 234 is disengaged from the groove, which causes a failure in turning the screw.
However, in either case described above, it is impossible to disassemble the driving piston 331 and the driver 330. Therefore, it is impossible to replace only the driver 330 when the driver 330 has worn away. In the former structure, in the case of a driving and turning machine, the driver 330 is turned together with the driving piston 331 after the completion of driving, and in the process of driving, a lower end of the driving piston 331 is pressed against the bumper 334 by the action of compressed air that has been fed into the driving cylinder 333, and further an upper end of the driver 330 is pressed against the driving piston 331, so that an intensity of rotational resistance is high with respect to the driving piston 331 and the driver 330. Therefore, it is necessary to increase an intensity of rotational drive force. On the other hand, in the latter case, the driver itself is turned, however, the structure becomes complicated and the manufacturing cost is raised. Further, since the driver 330 is integrally fixed to the piston 331 via the bearing 332, it is not easy to replace the driver 330.